Insects - Pests of Ornamental Trees, Shrubs and Flowers - page 38

Asterobemisia carpini (Koch)
syn. A. avellanae (Signoret); Aleurodes rubicola
(Douglas)
Hornbeam whitefly
Generally common in Europe on hornbeam ( Carpinus
betulus ) but also associated with other hosts, including
common hazel ( Corylus avellana ) and Rubus ; various
other plants are attacked in mainland Europe, including
maple ( Acer ), birch ( Betula ), beech ( Fagus sylvatica ),
false acacia ( Robinia pseudoacacia ) and Tilia ( lime ).
Eggs are laid on the underside of leaves in May and
June. The scale-like, pale yellowish to yellowish-green
nymphs then feed throughout the summer, completing
their development in the autumn. The insects overwinter
as pseudo-pupae, from which adults (which are
1.0-1.1 mm long, yellow or orange, with clear white
wings) emerge in the spring. Attacks on ornamental
plants are usually unimportant, although heavy
infestations cause foliage to become sticky with
honeydew and subsequently blackened by sooty
moulds.

nymphs suck plant sap from the underside of the leaves
of host plants, causing slight spotting of the tissue. The
insects excrete considerable quantities of honeydew.
The lifecycle is similar to that of Trialeurodes
vaporariorum (see p. 48) but development is slower for
any given temperature and may cease completely in the
winter, even in heated greenhouses. The pest is best
recognized as scattered yellow 'scales' (contrasting with
the more clumped distribution and paler 'scales' of
Trialeurodes vaporariorum ); also, eggs are laid singly
and randomly on the underside of the leaves.
Characteristically, the pseudo-pupae are slightly pointed
posteriorly and lack horizontally directed waxen
processes from the body wall; in repose, the wings of
adults are held in a sloping, roof-like posture. The pest
is a notorious virus vector.

Dialeurodes chittendeni Laing
Rhododendron whitefly
This locally distributed, generally uncommon European
whitefly is associated with Rhododendron , and is
sometimes a pest on R. campylocarpum, R. catawbiense,
R. caucasicum and R. ponticum ; other species or
cultivars where leaf cuticles are relatively thin or
unprotected by hairs or scales are also attacked. Adults
are 1.2 mm long, and pale yellow with pure white
wings. They occur in June and July and are relatively
sluggish, congregating on the underside of the leaves; if
disturbed, they fly only a short distance before
resettling. Eggs are laid singly on the underside of the
leaves of host plants but without any accompanying
waxy powder. Nymphs are flat and elliptical, greenish
yellow and semitransparent, without a waxy fringe.
They feed from mid-July onwards, surviving
throughout the winter; they 'pupate' in the following
spring, from mid-April onwards. The pseudo-pupae are
oval (1.2

Bemisia hancocki Corbett
A tropical and subtropical whitefly of uncertain status.
It infests the underside of the leaves of host plants,
including some ornamental species, and has been noted
in several parts of Europe, including England where it
was fist found on bay laurel ( Laurus nobilis ) in the
1970s. Rightly or wrongly, Bemisia hancocki is often
regarded merely as a synonym of Bemisia afer , a
polyphagous pest of cotton, peanut and other crops in
Africa and Asia.

Bemisia tabaci (Gennadius)
Tobacco whitefly
As an invasive alien species, this notorious tropical pest
has become established in several warmer parts of
Europe, including some Mediterranean countries. It
occurs from time to time on imported greenhouse plants
in northern European countries, such as England where
it is a quarantine pest. The insect has a very wide host
range but in northern Europe is most likely to occur on
ornamentals such as Gerbera, Gloxinia, Hibiscus and
poinsettia ( Euphorbia pulcherrima ), and on vegetable
crops such as sweet pepper and tomato. Adults and

0.9 mm), pale greenish yellow to whitish
yellow, also without a waxy fringe. Because of their
shape and colour, nymphs and pseudo-pupae are
difficult to see; however, following the emergence of
adults, the empty pseudo-pupal cases are more obvious.
Light infestations are of little or no significance.
However, if attacks are heavy, plant vigour is reduced,
infested foliage becoming mottled with yellow, and
covered with honeydew and sooty moulds.

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